In the semiconductor industry, the minimum feature sizes of microelectronic devices are approaching the deep sub-micron regime to meet the demand for faster, lower power microprocessors and digital circuits. Process development and integration issues are key challenges for new gate stack materials, where the replacement of SiO2 with high-k (where “k” refers to the dielectric constant of the material) dielectric materials can require the use of alternative gate electrode materials to replace doped poly-silicon (poly-Si).
The introduction of metal-containing gate electrodes to replace the traditional poly-Si gate can bring about several advantages. These advantages include elimination of the poly-Si gate depletion effect, reduction in sheet resistance, better reliability and potentially better thermal stability on advanced high-k dielectric gate materials. One of the material selection criteria for the metal-containing gate electrode is that the workfunction be adjustable. Control over the gate workfunction can be achieved using a composite metal-containing layer, where composition of the metal-containing layer can be adjusted to obtain the desired gate workfunction.